The present disclosure relates generally to blade outer air seals (BOAS) used in gas turbine engines, and more particularly to providing rapid response clearance control for the same.
Rotor tip clearance control is necessary for achieving improvements in turbomachinery efficiency and fuel consumption. It is desirable to minimize the clearance between a rotor tip and a static outer shroud seal (e.g., BOAS), while reducing the potential for tip rubbing during operation. This can be achieved by various means of active clearance control (ACC), which utilizes fluid, generally bleed air from a compressor exit and/or bypass duct of a gas turbine engine, to control the thermal expansion or contraction, and thereby the inner diameter, of an outer case. ACC is commonly used during cruising portions of a flight. Because thermal response can be slow, conventional ACC systems are generally not well suited to rapid throttle operations (e.g., snap accelerations, rapid re-accelerations, and maneuvers), which immediately add mechanical growth due to acceleration to the existing thermal growth of the rotor disk. During rapid throttle operations, the rotor and, in particular, the airfoil, can expand at a significantly higher rate than the case, requiring that tip clearances be set higher than desired to limit tip rubbing.
Clearance control assemblies capable of providing rapid response to thermal and mechanical growth are needed to reduce tip clearance during high throttle operations while reducing or preventing tip rub.